Alignment apparatus, exposure apparatus using same, and method of manufacturing devices

ABSTRACT

An alignment apparatus for aligning a reflective reticle includes a light source for emitting alignment light; an optical unit for guiding the alignment light, which has been emitted by the light source, to an alignment mark provided on the reticle and a reference mark provided on a reticle stage that holds the reticle; and detecting unit for detecting the alignment light reflected from the alignment mark and the reference mark, wherein the reticle is aligned on the basis of the result of detection by the detection unit.

FIELD OF THE INVENTION

[0001] This invention relates to a reticle alignment method in anexposure apparatus used in an exposure process for manufacturingsemiconductor integrated circuits, namely an alignment apparatus forachieving relative alignment between a reticle and the exposureapparatus per se, a method of controlling the alignment apparatus, aexposure apparatus for performing alignment of a reticle using thisapparatus, and a method of manufacturing semiconductor devices usingthis exposure apparatus.

BACKGROUND OF THE INVENTION

[0002] Demagnifying projection exposure using ultraviolet light has longbeen performed as a lithographic method for manufacturingmicro-semiconductor devices such as semiconductor memories and logiccircuits. The smallest dimensions that can be transferred bydemagnifying projection exposure are proportional to the wavelength ofthe light used in transfer and inversely proportional to the numericalaperture of the projection optics. In order to transfer microcircuitpatterns, therefore, shorter wavelengths are being adopted for the lightused. For example, the wavelength of ultraviolet light used has becomeprogressively shorter, i.e., 365 nm using mercury lamp i rays, 248 nmusing a KrF excimer laser and 193 nm using an ArF excimer laser.

[0003] However, semiconductor devices are becoming smaller and smallerat a rapid pace and lithography using ultraviolet light imposeslimitations on demagnifying projection exposure. Accordingly, in orderto perform the lithography of very fine circuit patterns of less than 1μm in an efficient manner, a demagnifying projection exposure apparatususing extreme ultraviolet (EUV) light having a wavelength on the orderof 10 to 15 nm, which is much shorter than that of ultraviolet light,has been developed.

[0004] Because absorption of light by substances is extremely high inthe EUV region, lens optics that utilize the refraction of light, asemployed with visible light and ultraviolet light, are impractical and,hence, use is made of reflective optical systems in exposure apparatusthat rely upon EUV light. These reflective optical systems employ areflective reticle obtained by forming the pattern, which is to betransferred, on a mirror using an absorbing body.

[0005] A multilayer mirror and an oblique-incidence full-reflectionmirror are examples of reflectance-type optical elements forconstructing an exposure apparatus that relies upon EUV light. In theEUV region, the real part of the index of refraction is much smallerthan unity and, as a result, total reflection occurs if use is made ofoblique incidence in which the EUV light just barely impinges upon themirror surface. Usually, a high reflectivity of 20 or 30% or more isobtained by oblique incidence of within several degrees measured fromthe surface. However, because such oblique incidence diminishes degreeof freedom in terms of optical design, it is difficult to use anoblique-incidence full-reflection mirror in a projection optical system.

[0006] A multilayer mirror obtained by building up alternating layers oftwo types of substances having different optical constants is used as amirror for EUV light employed at an angle of incidence close to that ofdirect incidence. For example, molybdenum and silicon are formed inalternating layers on the surface of a glass substrate polished to havea highly precise surface shape. The layer thicknesses of the molybdenumand silicon are, e.g., 0.2 nm and 0.5 nm, respectively, and the numberof layers is 20 each. The combined thickness of two layers of thedifferent substances is referred to as the “film cycle”. In the aboveexample, the film cycle is 0.2 nm+0.5 nm=0.7 nm.

[0007] When EUV light impinges upon such a multilayer mirror, EUV lightof a specific wavelength is reflected. Only EUV light of a narrowbandwidth centered on a wavelength X that satisfies the relationship ofBragg's equation

2×d×sin θ=λ  (1)

[0008] where λ represents the wavelength of the EUV light and d the filmcycle, will be reflected efficiently. The bandwidth in this case is 0.6to 1 nm.

[0009] The reflectivity of the reflected EUV light is 0.7 at most, andthe unreflected EUV light is absorbed in the multilayer films or in thesubstrate. Most of this energy is given off as heat.

[0010] Since a multilayer mirror exhibits more loss of light than amirror for visible light, it is necessary to hold the number of mirrorsto the minimum. In order to realize a broad exposure area using a smallnumber of mirrors, use is made of a method (scanning exposure) in whicha large area is transferred by causing a reticle and a wafer to performscanning using fine arcuate areas (ring fields) spaced apart from theoptical axis at fixed distances.

[0011]FIG. 8 is a schematic view illustrating a demagnifying projectionexposure apparatus that employs EUV light according to an example of theprior art. This apparatus includes an EUV light source, a illuminatingoptical system, a reflecting-type reticle, a projection optical system,a reticle stage, a wafer stage, an alignment optical system and a vacuumsystem.

[0012] By way of example, a laser plasma light source is used as the EUVlight source. Specifically, a target material placed in a vacuum vesselis irradiated with high-intensity pulsed laser light from a light source801, a high-temperature plasma is produced and EUV light having awavelength of, say, 13 nm that emanates from the plasma is utilized asthe EUV light source. A thin film of metal, an inert gas or a droplet isused as the target material, which is supplied by a target supply unit802, and is fed into the vacuum vessel by means such as a gas jet. Inorder to increase the average intensity of the EUV light emitted, thepulsed laser should have a high repetition frequency and the apparatusshould be operated at a repetition frequency of several kilohertz.

[0013] The illuminating optical system comprises a plurality ofmultilayer or oblique-incidence mirrors (803, 804, 805) and an opticalintegrator 806, etc. A condensing lens 803 constituting a first stagefunctions to collect EUV light that emanates from the laser plasmasubstantially isotropically. The optical integrator 806 functions toilluminate a reticle 814 uniformly using a prescribed numericalaperture. An aperture for limiting to a circular arc the area of thereticle surface that is illuminated is provided at a conjugate pointwith respect to the reticle 814 disposed in the illuminating opticalsystem.

[0014] The projection optical system uses a plurality of mirrors (808 to811). Though using a small number of mirrors allows EUV light to beutilized very efficiently, this makes it difficult to correct foraberration. The number of mirrors needed to correct for aberration isfour to six. The shapes of the reflecting surfaces of the mirrors areconvex or concave spherical or non-spherical. The numerical aperture NAis 0.1 to 0.3. To fabricate the mirror, use is made of a substrateconsisting of a material, such as glass having a low coefficient ofexpansion or silicon carbide, that exhibits a high rigidity and hardnessand a small coefficient of expansion, the substrate is formed to have areflecting surface of a predetermined shape by grinding and polishing,and multilayer films such as molybdenum and silicon are formed on thereflecting surface. In a case where the angle of incidence is notconstant owing to the location of the layer in the mirror surface, thewavelength of the EUV light, the reflectivity of which rises dependingupon the location, shifts if use is made of multilayer films having afixed film cycle, as is evident from Bragg's equation cited above.Accordingly, it is required that a film-cycle distribution be providedin such a manner that EUV light of the same wavelength will be reflectedefficiently at the mirror surface.

[0015] A reticle stage 812 and a wafer stage 813 have a mechanism inwhich scanning is performed synchronously at a speed ratio proportionalto the reducing magnification. Let X represent the scanning direction inthe plane of the reticle or wafer, Y the direction perpendicular to theX direction, and Z the direction perpendicular to the plane of thereticle or wafer.

[0016] The reticle 814 is held by a reticle chuck 815 on the reticlestage 812. The reticle stage 812 has a mechanism for high-speed movementin the X direction. Further, the reticle stage 812 has a fine-movementmechanism for fine movement in the X, Y and Z directions and for finerotation about these axes, thus making it possible to position thereticle. The position and attitude of the reticle stage are measured bylaser interferometers (not shown) and are controlled based upon theresults of measurement.

[0017] A wafer 816 is held by a wafer chuck 817 on the wafer stage 813.Like the reticle stage, the wafer stage 813 has a mechanism forhigh-speed movement in the X direction. Further, the wafer stage 813 hasa fine-movement mechanism for fine movement in the X, Y and Z directionsand for fine rotation about these axes, thus making it possible toposition the wafer. The position and attitude of the wafer stage aremeasured by laser interferometers (not shown) and are controlled basedupon the results of measurement.

[0018] Consider an arrangement in which an alignment detection system(818, 819) is implemented by an off-axis bright-field illuminated imageprocessing system similar to that of, e.g., an ArF exposure apparatus,and wafer alignment is carried out while a predetermined baseline amountis maintained.

[0019] Further, the focus position along the Z axis on the wafer surfaceis measured by a focus-position detecting optical system 820, and theposition and angle of the wafer stage are controlled. During exposure,therefore, the surface of the wafer is always maintained at the positionat which the image is formed by the projection optical system.

[0020] When a single scan of exposure of the wafer ends, the wafer stageis stepped in the X and Y directions to move the stage to the startingposition of the next exposure scan, then the reticle stage and waferstage are again scanned synchronously in the X direction at a speedratio that is proportional to the reducing magnification of theprojection optical system. Thus, an operation for synchronously scanningthe reticle and wafer in a state in which the demagnified projectionimage of the reticle is formed on the wafer is repeated (by astep-and-scan operation). The transfer pattern of the reticle is thustransferred to the entire surface of the wafer.

[0021]FIG. 9 is a diagram showing an arrangement for reticle alignmentaccording to the prior art. In the specification of this application,“reticle” and “mask” will be referred to generically as a “reticle”.

[0022] Reticle alignment involves achieving relative alignment between areticle reference mark 60, which has been positioned accurately on theapparatus proper, and a reticle alignment mark 4 situated on a reticle1. In FIG. 9, alignment light having a wavelength different from that ofthe exposing light is reflected on the side of the reticle side by aprism 80 and illuminates the reticle reference mark 60 and the reticlealignment mark 4. Light from the marks has the direction of its opticalpath changed by a deflecting mirror 70 and is directed toward an imagesensing device 10 via an optical system 40 so that the images of boththe reticle reference mark 60 and reticle alignment mark 4 are formed onthe image sensing device 10. Owing to the positional relationshipbetween the images of the two marks, the amount of positional deviationwith respect to the reticle 1 is calculated. Based upon the result ofcalculation, the reticle stage 812 is driven by a drive unit (not shown)to achieve alignment between the reticle alignment mark 4 and reticlereference mark 60. Performing this alignment completes the aligning ofthe reticle and exposure apparatus proper.

[0023] However, when reticle alignment in an X-ray demagnifyingprojection exposure apparatus (EUVL) is considered, the fact that thereticle used is a reflective reticle means that it is impossible todetect the mark images of both the reticle reference mark and reticlealignment mark simultaneously by “transmitting” the images.

[0024] Further, since the reflective reticle and multilayer mirror areoptimized so as furnish a high reflectivity with EUV light, there is thepossibility that a sufficient reflectivity will not be obtained for thealignment light, which is non-exposing light. In other words, in a casewhere consideration is given to so-called TTL (Through-the-Lens)alignment performed via a reflective reticle and a multilayer mirrorusing non-exposing light, there is the possibility that owing toalignment between the reticle alignment mark on the reflective reticleand the mark on the wafer, the image detection signal will declinebecause the the reticle alignment mark exhibits low reflectivity withrespect to alignment light.

[0025] In the ordinary projection exposure apparatus, a method ofaligning the reticle and wafer via a projection lens is referred to asTTL alignment. In an EUV exposure apparatus, however, the projectionoptical system is constituted not by lenses but by the multilayer-mirroroptical system. It is difficult, therefore, to refer to this scheme as aTTL scheme. However, for the sake of simplifying the description, analignment system that uses the intervention of a multilayer-mirroroptical system will also be defined as being a TTL alignment scheme inthis specification.

SUMMARY OF THE INVENTION

[0026] The present invention has been proposed to solve theaforementioned problems of the prior art and its feature is to providean alignment method and an alignment apparatus through which reticlealignment can be performed accurately even with regard to a reticle ofreflecting type, and through which a TTL alignment measurement in anexposure apparatus can also be performed in accurate fashion.

[0027] Another feature of the present invention is to provide anexposure apparatus in which alignment can be executed accurately andrapidly even in a case where use is made of a reticle involvinglimitations with regard to use of alignment light, such as areflecting-type reticle.

[0028] An alignment apparatus, and an exposure apparatus according tothe present invention are mainly provided with the followingconfiguration.

[0029] That is, the present invention provides an alignment apparatusfor aligning a reflective reticle, having:

[0030] a light source for emitting alignment light;

[0031] an optical unit for guiding the alignment light, which has beenemitted by the light source, to an alignment mark provided on thereticle and a reference mark provided on a reticle stage that holds thereticle;

[0032] detecting means for detecting the alignment light reflected fromthe alignment mark and the reference mark, and

[0033] wherein the reticle is aligned on the basis of the result ofdetection by the detection means.

[0034] Furthermore, the present invention provides an exposure apparatusfor exposing a substrate to a pattern of a reflective reticle, having:

[0035] a reticle stage for holding the reticle;

[0036] a substrate stage for holding the substrate;

[0037] an alignment light source for emitting alignment light having awavelength different from that of exposure light;

[0038] an optical unit for guiding the alignment light to an alignmentmark provided on the reticle and a reference mark provided on thereticle stage;

[0039] detecting means for detecting the alignment light reflected fromthe alignment mark and the reference mark; and

[0040] means for controlling the relative positions of the reticle andthe substrate on the basis of the result of detection by the detectionmeans.

[0041] Furthermore, the present invention provides an exposure apparatusfor performing exposure using exposure light, the apparatus employing areticle holding mechanism for holding a reticle, a substrate holdingmechanism for holding a substrate to be exposed, and a projectionoptical system for projecting a pattern of the reticle onto thesubstrate to thereby expose the substrate to the pattern, having:

[0042] first position detection unit for detecting a position referenceof the reticle holding mechanism;

[0043] second position detection unit for detecting a position referenceof the substrate holding mechanism; and

[0044] a third position detection unit for detecting both the positionreference of the reticle holding mechanism and the position reference ofthe substrate holding mechanism via the projection optical system;

[0045] a baseline on the side of the reticle holding mechanism beingfound from results of detection by the first and third positiondetection units, a baseline on the side of the substrate holdingmechanism being found from results of detection by the second and thirdposition detection units, and relative positions of the reticle holdingmechanism and the substrate holding mechanism being controlled using thefirst and second position detection units upon taking both of thebaselines into consideration.

[0046] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0048]FIG. 1 is a schematic side view of an alignment apparatus andillustrates reticle alignment according to the present invention;

[0049]FIG. 2 is a diagram useful in describing reticle alignmentprocessing according to the present invention;

[0050]FIG. 3 is a diagram useful in describing reticle alignmentprocessing according to the present invention;

[0051]FIG. 4 is a diagram useful in describing a second embodiment ofthe present invention;

[0052]FIG. 5 is a diagram showing an arrangement in a case where analignment apparatus is applied to an EUV exposure apparatus;

[0053]FIG. 6 is a diagram useful in describing the flow of a devicemanufacturing process;

[0054]FIG. 7 is a diagram useful in describing the details of a waferprocess;

[0055]FIG. 8 is a diagram showing the structure of an EUV exposureapparatus according to the prior art;

[0056]FIG. 9 is a diagram showing reticle alignment according to theprior art; and

[0057]FIG. 10 is a flowchart showing an overview of processingillustrative of the procedure of an alignment method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Preferred embodiments of the present invention will now bedescribed in detail in accordance with the accompanying drawings.

[0059] <First Embodiment>

[0060]FIG. 1 is a diagram useful in describing a first embodiment of analignment apparatus according to the present invention. This diagramillustrates reticle alignment in a demagnifying X-ray exposure apparatus(EUV). Reticle alignment is characterized by scanning a reticle stage 6to detect, in the form of an image, a positional deviation betweenreticle-stage reference marks (2, 3) on the reticle stage 6 and reticlealignment marks (4, 5) on a reticle 1. FIG. 10 is a flowchart showing anoverview of processing illustrative of the procedure of an alignmentmethod.

[0061] The details of this processing will now be described. Alignmentlight having a wavelength different from that of exposing light isemitted from an illumination source 20 (step S1010). The alignment lighthas its direction changed by the optical system 40 (step S1020) and isguided to a deflecting mirror 50. The deflecting mirror 50 is placed inan area where it will not block the exposing light. The mirror 50 can befixed at this position or can be moved. The alignment light that has hadthe direction of its optical path changed by the deflecting mirror 50 issuch that its principal ray impinges vertically upon the reticle stage 6and reticle 1 (step S1030).

[0062] Alignment light that has been reflected by the reticle-stagereference mark 2 on the reticle stage 6 is directed toward the imagesensing device 10 via the deflecting mirror 50 and optical system 40 sothat the image of the reticle-stage reference mark 2 is formed on theimage sensing device 10.

[0063] Next, the reticle stage 6 is scanned a predetermined amount in apredetermined direction so that the images of the reticle alignmentmarks 4, 5 and reticle-stage reference mark 3 are formed on the imagesensing device 10 (step S1040). The positional deviations of theseimages are then calculated (step S1050). It should be noted that thereticle-stage reference marks 2, 3 and reticle alignment marks 4, 5 aresituated at the same height along the Z direction beforehand for theconvenience of the arrangement. However, the defocusing characteristicsof each of the mark images may be detected to detect height along the Zdirection.

[0064] It should be noted that the reticle reference mark 60 has beenpositioned accurately on the apparatus proper and that the image of thereticle reference mark 60 is formed on the image sensing device 10 byilluminating light from another illumination source 30, thereby makingit possible to measure periodically the aging of the detection opticalsystem inclusive of the image sensing device 10.

[0065] Further, since the reticle-stage reference marks 2, 3 have beendisposed on the reticle stage 6, a temporal change in traveling error ofthe reticle stage in the scanning direction can be observed in“reticleless” fashion (i.e., in a state in which the reticle stage isdevoid of a reticle). By ascertaining such change with the passage oftime, it is possible to calibrate positioning of the stage.

[0066]FIG. 2 is a plan view illustrating EUV reticle alignment in whichplacement of the reference marks is seen from the Z direction. First,two or more reticle-stage reference marks are placed on the reticlestage 6. Further, two or more reticle alignment marks on the reticle 1are placed in an area away from the exposure area. For example, thereticle-stage reference marks are represented by MS1 to MS4, and thereticle alignment marks are represented by MA1 to MA 4.

[0067] Furthermore, image sensing devices 200, 201 in FIG. 2 are placedat locations that have been positioned accurately in the apparatusproper. While the reticle stage is scanned in the negative directionalong the X axis, deviation of the reticle alignment marks with respectto the reticle-stage reference marks, namely deviation of the reticle,can be calculated from the amounts of positional deviation of the markswhose images have been formed on the image sensing devices 200, 201.More specifically, the reticle stage 6 is scanned in the negativedirection along the X axis and the reticle-stage reference marks MS1,MS2 on the reticle stage are detected using the image sensing devices200, 201. This detection method obtains the currently prevailing amountsof deviation from the centers of the image sensing devices 200, 201using bright-field image processing.

[0068] Next, if the reticle 1 has been placed on the reticle stage inaccordance with design values, the reticle stage is scanned in thenegative direction along the X axis in such a manner that the reticlealignment marks MA1 to MA 4 will arrive directly below the image sensingdevices 200, 201, and bright-field image processing is used to findpositional deviation amounts (X1, Y1) to (X4, Y4) of the reticlealignment marks MA1 to MA4 and positional deviation amounts of thereticle-stage reference marks MS3, MS4 whose images have been formed onthe image sensing devices 200, 201. Finally, deviation of the reticlealignment marks with respect to the reticle-stage reference marks,namely the amount of deviation of the reticle, is calculated. Thisdeviation is added to an alignment control variable as deviation from acase where the reticle has been disposed on the reticle stage normallywhen the reticle and wafer are aligned utilizing the reticle-stagereference marks and wafer-stage reference marks, as will be describedlater. An arrangement may be adopted in which a correction is applied byutilizing this deviation to displace the reticle stage so as to placethe reticle at the position of the design values or to re-dispositionthe reticle on the reticle stage (using a reticle transport mechanism,which is not shown) to obtain the stipulated layout.

[0069]FIG. 3 is a diagram useful in describing a specific reticlealignment operation in the positioning apparatus of the presentinvention. In order to execute alignment, any two points are selected asreference marks and a geometric positional relationship between thesereference marks and the image sensing devices 200, 201, is calculated.Let the amounts of positional deviation of selected reticle alignmentmarks MA1 and MA2 be (X1, Y1) and (X2, Y2), respectively. If reticledeviation amounts (X, Y, θ) are calculated using the positionaldeviation amounts of the reticle alignment marks MA1, MA2, theoperations are as follows:

X ₁ =X+R ₁θ sin θ₁   (2)

Y ₁ =Y+R ₁θ cos θ₁

X ₂ =X−R ₂θ sin θ₂   (3)

Y ₂ =Y+R ₂θ cos θ₂

[0070] From these equations, we obtain the following: $\begin{matrix}{X = \frac{{R_{2}\sin \quad \theta_{2}X_{1}} + {R_{1}\sin \quad \theta_{1}X_{2}}}{{R_{1}\sin \quad \theta_{1}} + {R_{2}\sin \quad \theta_{2}}}} & (4) \\{\theta = \frac{X_{1} - X_{2}}{{R_{1}\sin \quad \theta_{1}} + {R_{2}\sin \quad \theta_{2}}}} & (5) \\{Y = \frac{{R_{2}\cos \quad \theta_{2}Y_{1}} + {R_{1}\cos \quad \theta_{1}Y_{2}}}{{R_{2}\cos \quad \theta_{2}} + {R_{1}\cos \quad \theta_{1}}}} & (6)\end{matrix}$

[0071] In order to calculate the reticle deviation amounts (X, Y, θ), itsuffices to make the calculation if two measurement points lie in aplane. However, it is also possible to calculate the reticle deviationamounts (X, Y, θ) by sensing the amounts of positional deviation of,e.g., the reticle alignment marks MA3, MA4 in the form of images usingthe image sensing devices and calculating the positional deviationamounts (X3, Y3), (X4, Y4). Further, statistical processing is possibleby multiple-point measurement, as in this embodiment. Advantageouseffects can be achieved, an averaging effect.

[0072] <Second Embodiment>

[0073]FIG. 4 is a diagram useful in describing a second embodiment of analignment apparatus and method according to the present invention.Whereas FIG. 2 illustrates an arrangement in which two image sensingdevices 200, 201 are disposed in the negative direction along the Xaxis, there is no limitation on the placement of the image sensingdevices in this embodiment; image sensing devices 202, 203 may also beplaced in the positive direction along the X axis, as depicted in FIG.4. When the reticle stage is scanned in the negative direction along theX axis, the image sensing devices 200, 201 can be used to detect thereticle-stage reference marks MS1, MS2 and reticle alignment marks MA1,MA2. When the reticle stage is scanned in the positive direction alongthe X axis, the image sensing devices 202, 203 can be used to detect thereticle-stage reference marks MS3, MS4 and reticle alignment marks MA3,MA4. As a result, alignment detection is possible using only a scanningarea necessary for the reticle stage to be exposed to EUV light, errordue to unnecessary scanning of the reticle stage is reduced andprecision can be improved further.

[0074] With conventional reticle alignment, as shown in FIG. 9, makingthe gap between the reticle reference mark 60 and reticle alignment mark4 too large is undesirable for reasons of precision. With reticlealignment according to the first and second embodiments, however, theworking distance between the deflecting mirror 50 and reticle-stagereference mark 2 may be chosen freely. This affords greater freedom ofdesign with regard to the pellicle on the reticle.

[0075] <Third Embodiment>

[0076]FIG. 5 is a diagram illustrating the structure of an exposureapparatus that includes an alignment device and is useful in describinga third embodiment. Image sensing devices 10 a, 10 b, illuminationsources 20 a, 20 b, illumination sources 30 a, 30 b, optical systems 40a, 40 b, a deflecting mirror 50 a and reticle reference marks 60 a, 60 bare members corresponding to the above-described image sensing device10, illumination source 20, illumination source 30, optical system 40,deflecting mirror 50 and reticle reference mark 60, respectively. Theapparatus further includes a wafer chuck 110 for holding a wafer 100, aθZ tilt stage 120 and an XY stage 130. While the wafer 100 isilluminated with EUV light, which is exposing light from an illuminationsystem 80, via the reticle 1 and a reflecting-mirror optical system 90,the reticle stage 6 and XY stage 130 (the θZ tilt stage 120 also isused) are scanned synchronously, whereby the wafer 100 is exposed to thepattern on the reticle 1 by scanning projection. Alignment light, whichis non-exposing light, is emitted from the illumination source 20 b. Thenon-exposing light is reflected by a mirror 50 b, thereby illuminatingthe reticle-stage reference mark 2. Furthermore, the alignment lightreflected by the reticle-stage reference mark 2 passes through thereflecting-mirror optical system 90 and illuminates a stage referencemark 140 on the wafer stage.

[0077] Alignment light reflected by the stage reference mark 140 passesthrough the reflecting-mirror optical system 90 again and is reflectedby the reticle-stage reference mark 2, after which the light isreflected by the mirror 50 b and directed toward the image sensingdevice 10 b. The reticle and wafer are brought into alignment based uponthe relative positional relationship between the detected stagereference mark 140 and reticle-stage reference mark 2. (In thisspecification, this is covered by the definition of on-axis TTLalignment.)

[0078] Here the relative positional relationship between the reticle 1and the reticle-stage reference mark 2 is detected beforehand by themethod described in the first embodiment. With regard to the positionalrelationship between the two, it is assumed that alignment has beenperformed accurately or that the state of deviation has been ascertainedcorrectly.

[0079] Next, in similar fashion, the relative positional relationshipbetween the stage reference mark 140 and a wafer alignment mark (notshown) on the wafer 100 is detected separately by an off-axis methodusing an off-axis scope in which image sensing is performed by the imagesensing device 150 via the optical system 160, and alignment isperformed or the state of deviation ascertained.

[0080] Next, the distance (baseline), which corresponds to ΔA in FIG. 5,between the exposure axis and off-axis detection system is found using awell-known baseline measurement method. More specifically, and by way ofexample, ΔA can be calculated accurately from the position of the stagereference mark 140 detected by the non-exposing alignment light emittedfrom the illumination source 20 b, the position of the stage referencemark 140 detected using the off-axis microscope, and the stagetravelling distance between the detected positions.

[0081] Furthermore, in this embodiment, reticle alignment also isperformed at a location offset from the exposure axis and, hence, thereis a distance, which corresponds to ΔB in FIG. 5, between the exposureaxis and the reticle alignment detection system. This is defined as thebaseline on the reticle side. The baseline ΔB on the reticle side canalso be detected accurately in a manner similar to that of ordinarybaseline calculation by detecting the position of the reticle-stagereference mark 2 using non-exposing alignment light emitted from theillumination source 20 b and detecting this position by the detectionsystem described in the first embodiment.

[0082] In this embodiment, off-axis TTL alignment is carried out andbaselines on the sides of the reticle and wafer are corrected, wherebythe alignment relationship among the exposure axis and the off-axisdetection systems on the reticle and wafer sides is determined.Accordingly, if the positional relationship between reticle-stagereference mark and reticle alignment mark is detected by the method ofthe first embodiment whenever the reticle is changed or periodically,and the positional relationship between the stage reference mark andwafer alignment mark is detected by the above-mentioned off-axis scopewhenever the wafer is changed, then, upon subsequently adding all ofthese mutual interrelationships together, the reticle 1 and wafer 100can be aligned by performing so-called off-axis global alignment, inwhich relative alignment is executed by relying upon the precision ofstage movement using as a reference the positions of the reticle-stagereference mark 2 and stage reference mark 140 obtained by each of theoff-axis systems. In this case, it will suffice to use on-axis TTLalignment only for checking the baselines. Moreover, in the abovedescription, though the reticle alignment mark and the reticle referencemark are also used as the reflected type, even if it is the case whereat least one side is a transmitted type, the baseline ΔB can also bedetected by the similar method.

[0083] In this embodiment, through a technique different from the above,the positional relationship between the reticle-stage reference mark andreticle alignment mark can be detected by the method of the firstembodiment whenever the reticle is changed or periodically, and thepositional relationship between the stage reference mark and waferalignment mark can be detected by the above-mentioned off-axis scopewhenever the wafer is changed, and then on-axis TTL alignment can beperformed each time wafer exposure is performed. In this case, relativealignment (global alignment) that relies upon the precision of stagemovement can be executed based upon the result of position detection byon-axis TTL. Baseline measurement is not required. It should be notedthat the mirror 50 b has a moving mechanism so that it will not blockthe EUV exposing light emitted from the illumination system 80. Further,it is particularly desirable to adopt an arrangement in which aplurality of wafer alignment marks and a plurality of stage referencemarks are also provided on the reticle side in similar fashion and aredetected by respective ones of a plurality of off-axis scopes.

[0084] In accordance with this embodiment, as shown in FIG. 5, thereference on the reticle side necessary for on-axis TTL alignment can beshifted from the reticle alignment mark, for which reflectivity, i.e.,mark contrast, is poor with non-exposing light, to the reticle-stagereference mark. As a result, on-axis TTL alignment can be carried outusing a reticle-stage reference mark for which reflectivity (markcontrast) is optimized with respect to alignment light, and alignmentprecision therefore is improved. In particular, according to thisembodiment, the light source for detecting the reticle-stage referencemark and stage reference mark via the reflecting-mirror optical system,the light source for detecting the reticle-stage reference mark andreticle alignment mark, and the light source for detecting the stagereference mark and wafer alignment mark are separate light sources. As aresult, the wavelength of light suited to on-axis TTL alignment and thewavelengths of light suited to detection of the reticle mark anddetection of the wafer mark can be selected separately.

[0085] <Fourth Embodiment>

[0086] Described next will be an embodiment of a method of manufacturinga device utilizing the exposure apparatus set forth above. FIG. 6 is aflowchart illustrating the manufacture of a microdevice (a semiconductorchip such as an IC or LSI, a liquid crystal panel, a CCD, a thin-filmmagnetic head, a micromachine, etc.).

[0087] The circuit for the device is designed at step 1 (circuitdesign). A mask on which the designed circuit pattern has been formed isfabricated at step 2 (mask fabrication). Meanwhile, a wafer ismanufactured using a material such as silicon or glass at step 3 (wafermanufacture). The actual circuit is formed on the wafer by lithography,using the mask and wafer that have been prepared, at step 4 (waferprocess), which is also referred to as “pre-treatment”. A semiconductorchip is obtained, using the wafer fabricated at step 4, at step 5(assembly), which is also referred to as “post-treatment”. This stepincludes steps such as actual assembly (dicing and bonding) andpackaging (chip encapsulation). The semiconductor device fabricated atstep 5 is subjected to inspections such as an operation verificationtest and durability test at step 6 (inspection). The semiconductordevice is completed through these steps and then is shipped (step 7).

[0088]FIG. 7 is a flowchart illustrating the detailed flow of the waferprocess mentioned above. The surface of the wafer is oxidized at step 11(oxidation). An insulating film is formed on the wafer surface at step12 (CVD), electrodes are formed on the wafer by vapor deposition at step13 (electrode formation), and ions are implanted in the wafer at step 14(ion implantation). The wafer is coated with a photoresist at step 15(resist treatment), the wafer is exposed to the circuit pattern of themask to print the pattern onto the wafer by the above-described exposureapparatus at step 16 (exposure), and the exposed wafer is developed atstep 17 (development). Portions other than the developed photoresist areetched away at step 18 (etching), and unnecessary resist left afteretching is performed is removed at step 19 (resist removal). Multiplecircuit patterns are formed on the wafer by implementing these stepsrepeatedly.

[0089] If the manufacturing method of this embodiment is used, it willbe possible to manufacture semiconductor devices having a high degree ofintegration. Such devices have been difficult to manufacture heretofore.

[0090] In accordance with the present invention, as described above,reticle alignment can be achieved using the reticle stage as areference. This makes possible alignment that is not affected by thereflectivity of the reticle.

[0091] Further, in accordance with the present invention, the referenceon the reticle side necessary for on-axis TTL alignment can be shiftedfrom the reticle alignment mark to the reticle-stage reference mark. Asa result, on-axis TTL alignment can be carried out using a reticle-stagereference mark for which reflectivity is optimized with respect toalignment light, and alignment precision therefore is improved.

[0092] In accordance with the present invention in a separate aspect,alignment can be executed accurately and rapidly based upon a referencemark provided on a stage even in a case where use is made of a reticleinvolving limitations with regard to use of alignment light, such as areflecting-type reticle.

[0093] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An alignment apparatus for aligning a reflectivereticle, having: a light source for emitting alignment light; an opticalunit for guiding the alignment light, which has been emitted by thelight source, to an alignment mark provided on the reticle and areference mark provided on a reticle stage that holds the reticle;detecting means for detecting the alignment light reflected from thealignment mark and the reference mark; and wherein the reticle isaligned on the basis of the result of detection by the detection means.2. An alignment apparatus according to claim 1, wherein a plurality ofthe alignment marks are provided on the reticle.
 3. An alignmentapparatus according to claim 1, wherein the optical unit guides thealignment light substantially perpendicularly with respect to thealignment mark and reference mark.
 4. An alignment apparatus accordingto claim 1, wherein the reticle is a reticle for a exposure apparatus.5. An exposure apparatus for exposing a substrate to a pattern of areflective reticle, having: a reticle stage for holding the reticle; asubstrate stage for holding the substrate; an alignment light source foremitting alignment light having a wavelength different from that ofexposure light; an optical unit for guiding the alignment light to analignment mark provided on the reticle and a reference mark provided onthe reticle stage; detecting means for detecting the alignment lightreflected from the alignment mark and the reference mark; and means forcontrolling the relative positions of the reticle and the substrate onthe basis of the result of detection by the detection means.
 6. A methodof manufacturing a device, having: a step of exposing a substrate usingan exposure apparatus according to claim 5; and a step of developing thesubstrate.
 7. An exposure apparatus for performing exposure usingexposure light, said apparatus employing a reticle holding mechanism forholding a reticle, a substrate holding mechanism for holding a substrateto be exposed, and a projection optical system for projecting a patternof the reticle onto the substrate to thereby expose the substrate to thepattern, having: first position detection unit for detecting a positionreference of said reticle holding mechanism; second position detectionunit for detecting a position reference of said substrate holdingmechanism; and a third position detection unit for detecting both theposition reference of said reticle holding mechanism and the positionreference of said substrate holding mechanism via said projectionoptical system; a baseline on the side of said reticle holding mechanismbeing found from results of detection by said first and third positiondetection units, a baseline on the side of said substrate holdingmechanism being found from results of detection by said second and thirdposition detection units, and relative positions of said reticle holdingmechanism and said substrate holding mechanism being controlled usingsaid first and second position detection units upon taking both of saidbaselines into consideration.
 8. An exposure apparatus according toclaim 7, wherein the first position detection unit detects a relativepositional relationship between the position reference of said reticleholding mechanism and a reticle alignment mark, the second positiondetection unit detects a relative positional relationship between theposition reference of said substrate holding mechanism and a substratealignment mark, and relative alignment between the reticle and substratebeing executed based upon both of the relative positional relationshipsobtained.
 9. An exposure apparatus according to claim 7, wherein thereticle is reflective reticle.
 10. An exposure apparatus according toclaim 7, wherein the position reference of said reticle holdingmechanism is a reticle reference mark provided on the reticle stage,wherein the reticle reference mark is reflective reticle.
 11. Anexposure apparatus according to claim 7, wherein X rays are adopted asthe exposure light.
 12. A method of manufacturing a device, having: astep of exposing a substrate using an exposure apparatus according toclaim 7; and a step of developing the substrate.